Known conventional switching devices include power semiconductor devices for large current applications such as IGBTs (Insulated Gate Bipolar Transistor), power MOS-FETs, and power transistors, etc. Meanwhile, hybrid cars and electric cars have drawn attention in recent years from the viewpoint of environment preservation or the like. An inverter device mounted in such a hybrid vehicle or the like is configured, for example, primarily with IGBT devices soldered on an insulating substrate, this insulating substrate with IGBT devices joined thereon being soldered to a base member that forms a housing of the inverter device.
The IGBT devices joined to the base member via the insulating substrate are electrically connected to a circuit wiring or other electronic components, etc formed on the base member by metal conductors.
Aluminum wires, for example, are used as the metal conductors for connecting the IGBT devices with other circuit wirings. The aluminum wire is bonded by wire bonding to the IGBT devices and other circuit wirings, etc to connect them.
Because of the recent demand for IGBT devices with higher current density, a sufficient area needs to be secured for the metal conductors and their joints since a large current will flow through the metal conductors connecting the IGBT devices with other circuit wirings, etc. To secure the area, typically, the number of wires, or the bonding area per one wire will have to be increased. Since an increase in the number of wires leads to an increase in the processing cost, metal conductors formed in a tape-like shape (wide, thin plate-like shape) to have a larger cross-sectional area (tape material) are increasingly used instead of wires having larger electrical resistance.
When connecting an IGBT device with another circuit wiring, etc with a wire or tape material, the wire or tape material is brought into contact with a wiring terminal of the IGBT device or another circuit wiring, and in this state, using a bonding tool of a bonding apparatus, for example, it is subjected to pressing load and ultrasonic vibration, whereby the wire or tape material is ultrasonically joined to the wiring terminal of the IGBT device or another circuit wiring.
The joint between the wire or tape material and the wiring terminal of the IGBT device is evaluated by, for example, detecting ultrasound applied to the bonding tool, and by comparing a detected ultrasound waveform with a predetermined reference ultrasound waveform (see Patent Document 1). The joint may also be evaluated by detecting the height of a lead wire (metal conductor) from the bonding surface and by determining whether or not the height is within a predetermined range (see Patent Document 2).